A module for processing ATM cells of a cell flow on virtual channels and virtual paths that is configured for recognizing error conditions in the ATM inventory and for inserting OAM-specific cells for the generation of which an OAM generator (OZG) is provided.
ATM, the abbreviation for xe2x80x9casynchronous transfer modexe2x80x9d, is a network technology that is suitable for the transport of all known signal data such as pure data, voice and video data, etc., whereby the designation ATM is occasionally employed as a synonym for B-ISDN (broadband integrated services digital network). The structuring into cells of equal length is characteristic of ATM. The information to be mediated is divided onto ATM cells, namely into packets of 53 bytes that carry a cell header (header) with 5 bytes and payload information (payload) with 48 bytes. The header information thereby identifies a specific virtual connection. In contrast to traditional time-division multiplex methods wherein time slots are allocated in advance to different types of data traffic, the incoming data traffic at an ATM interface is segmented into the 53-byte cells, and these cells are sequentially forwarded as they were generated. Further details about ATM can be derived from the literature. Let xe2x80x9cATM networks, concepts, protocols and applicationsxe2x80x9d, by Hxc3xa4ndel, Huber and Schrxc3x6der, Addison-Wesley-Longman, 2nd Edition, 1994 (ISBN 0-201-42274-3) or xe2x80x9cATM-Solutions for Enterprise Internet Workingxe2x80x9d by D. Ginsburg be cited by way of example.
LSI circuits in ASIC components are employed for processing ATM cells. OAM modules are one example, these being utilized for the administration and processing of the OAM flows (OAM=operation administration and maintenance). OAM modules or other cell processing modules are utilized, for example, between network matching units and a switching network module or other modules. FIG. 1 is referenced in this respect, this showing a possible architecture. Physical layer modules PHY can be seen at the left and right in the Fig., these enabling the transition from a transport network, for example STM1, onto ATM. The dot-dashed lines at the left and right symbolize the boundaries between the physical layer Phy. L. and the ATM layer ATM-L. ATM modules BST are provided symmetrically relative to the switching network module SWI, these lying between the switching network module SWI and the physical layer modules PHY. Dependent on the demands and conditions, one or more ATM modules BST can be present. In order to indicate this, a respective ATM module is shown with broken lines.
As can be derived from the block circuit diagram of FIG. 1, which is relevant both for the prior art as well as for the invention, bidirectional data streams are processed, these being referenced AUF for upstream and AB for downstream. The original English names xe2x80x9cupstreamxe2x80x9d and xe2x80x9cdownstreamxe2x80x9d in switching networks indicate the direction xe2x80x9cup toxe2x80x9d the switching network or, respectively, xe2x80x9cdown fromxe2x80x9d the switching network. Fundamentally, however, the designations of the two data streams as AUF and AB are arbitrary and can be interchanged. Below, the data or, cell streams arriving at a module shall be referenced ZI and the outgoing cell streams shall be referenced ZA both upstream as well as downstream. Transverse channels that are arranged at the transverse channel inputs QI as well as transverse channel outputs QA of the modules are respectively present between two modules BST for upstream and downstream.
In order to be able to control an ATM module BST, a control software is also indicated with the assistance of the block STSW in FIG. 1. It is needed for the configuration of an ATM module, for the error handling and the setup and release of connections. The control software normally runs on a commercially obtainable processor module. The control software STSW is connected to the ATM module BST via what is referred to as an interrupt signal I and a bidirectional control bus CB. The interrupt signal I serves the purpose of stopping the software in order to inform it of time-critical events that have occurred in the ATM module BST (for example, recognized error conditions).
The job of the ATM layer ATM-L that, for example, is explained in greater detail in the references cited above is to enable the transparent transfer of ATM cells via pre-established connections and it is concentrated on the data base unit, namely the 53-byte ATM cell (or xe2x80x9coctetxe2x80x9d). A five-layer hierarchy exists for OAM flows; this, for example, can be derived from the references and from ITU Recommendation G.610. The ATM layers F4 for the virtual path level and F5 for the virtual channel level are determinant for the present invention.
Critical jobs of the OAM flows include the error recognition, error localization and error message. Special cells are allocated to specific OAM flows; the AIS cells, the RDI cells and the CC cells shall be considered here. Error statuses in the physical layer and the ATM layer lead to error messages with the assistance of these special cells. The F4 flows and the F5 flows must thereby be handled independently of one another.
In the direction toward the end point of the connection on the channel or path, errors are signaled by the AIS cells (alarm indication signal cells), by contrast whereto the RDI cells (remote defect indication cells) serve this purpose in the direction toward the start point of a connection. When error conditions are recognized, they must be forwarded within 500 ms for all existing connections according to the ITU Recommendations G.610. A respective AIS OR RDI cell must be utilized per connection in the error status, whereby, for example, 8000 connections can be present.
In order to be able to constantly monitor the continuity of a connection, CC cells (continuity check) are utilized at the start point of a connection or of a segment, particularly when ATM user cells were not transmitted. A check can then be carried out at the end point of a connection or of a segment to see whether user or CC cells have arrived within a predetermined time interval. When this is not the case, then the corresponding connection switches into a specific error status (loss of continuity) that leads to the above-described insertion of AIS or RDI cells.
The handling of the OAM functions AIS, RDI and CC is currently essentially incremented in the softwarexe2x80x94for the purpose, too, of administering the statuses for the individual connections and the linking of these functions to one anotherxe2x80x94, whereby all incoming OAM cells are first made available to the software. The required software expense is so high that the regulations of ITU 610 cannot be adhered to in a great number of connections.
An object of the invention is comprised in more economically enabling the processing of the OAM functions and thereby keeping the overall expense for hardware and software low.
This object is achieved with a module wherein, according to the invention, a cell filter and processing unit to which the incoming cell stream is supplied, a connection data memory in communication with the cell filter and processing unit, a scan unit in communication with the connection data memory and to which a controller and a request counter are allocated, an intermediate buffer whose input is connected to the output of the OAM cell generator, a status buffer that is established for the transmission of the status information to the control software, as well as a multiplexer to which the output of the cell filter and processing unit as well as the output of the intermediate buffer are supplied. The cell filter and processing unit is configured for recognizing the cell type and for outputting cell recognition signals as well as a connection index pertaining to the respective connection to the connection data memory, and is also configured for forwarding received cells to the multiplexer dependent on the recognized cell type and the configuration data. The controller is configured for outputting a start signal for the scan mechanism to the scan unit, so that the sequential processing of all active connections by the scan unit is started at regular time intervals, whereby an interpretation of the cell recognition signals and of status signals and the generation of new or, revised status signals occurs. The scan unit (SCAN) is configured for outputting a request signal to the OAM cell generator that contains the exact type of OAM cell to be generated as well as the necessary connection data for the cell header.
The invention offers the advantage that the handling of the OAM functions, particularly the functions RDI, AIS and CC and their linkages to one another, can be implemented in the hardware. The software is merely informed of status changes via a specific interrupt signal I and the control bus CB. The OAM handling is thus not dependent on the momentary load condition of the SW. This results in the requirements according to ITU 610 always being assured even given the appearance of many error statuses and given a great number of existing connectionsxe2x80x94for example, 8000 active connections.
It is provided in an expedient embodiment that the intermediate buffer is established for outputting a hold signal to the scan unit when it fills up, as a result whereof short-term overloads can be intercepted on the part of the control software or, respectively, the cell filter and processing unit or a transverse channel.
It is recommended for the function of the scan unit when a request counter is provided that, with the assistance of a counter status signal of the scan unit, indicates the number of connections that are allowed to be successively processed, whereby the value of the request counter is lowered by 1 on demand by the scan unit after processing a connection in the current cycle.
For the purpose of a uniform distribution of processing the individual connections, it is advantageous when a cycle counter is provided whose value is set to zero when the scan unit starts, as is the value of the request counter, and the scan unit or, the block LB is configured for incrementing the value of the request counter by 1 and resetting the cycle counter to zero when the value of the cycle counter has reached an adjustable cycle duration.
In another preferred version, the multiplexer comprises a transverse channel from a module of the opposite direction.
The module of the invention is configured for processing the OAM functions AIS, RDI and CC with particular advantages in view of the processing economy.
The invention together with further advantages thereof is explained in greater detail below with reference to exemplary embodiments and the assistance of the drawings that are illustrated in the drawing [sic].